1. Field of the Invention
The present invention relates to a polymer electrolyte fuel cell and more specifically, to the polymer electrolyte fuel cell whose passage is prevented from being blocked by condensed water.
2. Detailed Description of the Prior Art
A polymer electrolyte fuel cell is basically so arranged that an anode and a cathode are provided, with an electrolytic polymer electrolyte film interposed in-between; a fuel gas containing hydrogen is caused to flow on the anode side; and an oxidant gas containing oxygen is caused to flow on the cathode side; thereby generating electricity and water through electrochemical reaction.
In this arrangement, cooled water is supplied to humidify fuel gas or oxidant gas for the purpose of enhancing the electric conductivity of the polymer electrolyte membrane. The resulting humidification not only causes the polymer electrolyte membrane to be wetted but also lowers the heat generated by the exothermic reaction of the fuel cell.
FIG. 8 shows an example of a prior art polymer electrolyte fuel cell wherein:
a plate A, a plate B, and a plate C are used;
a cell D is disposed on the front side of the plate A;
another cell D is disposed on the rear side of the plate A;
a permeable film E is disposed on the rear side of the plate B (on the other side than that side of the plate B which is opposite a cell D);
another permeable film E is disposed on the front side of the plate C (on the other side than that side of the plate C which is opposite a cell D);
a cell unit is thus formed;
a plurality of such cell units are integrally stacked to form a polymer electrolyte fuel cell; and
a humidifying chamber F is provided between two adjacent cell units, namely between the plate C and a plate (B).
A passage is formed on each of the front and rear sides of each of the plates A, B, and C (Axe2x80x3, Bxe2x80x3, and Cxe2x80x3 denote the rear side of the plate A, the rear side of the plate B, and the rear side of the plate C, respectively). Fuel gas, which is supplied from a lateral portion of the polymer electrolyte fuel cell, flows in through a fuel inlet B1, and is discharged through a fuel outlet B2 after passing through a fuel chamber disposed on the anode side of each of the cells D. Oxidant gas flows in through an oxidant inlet B3, and is discharged through an oxidant outlet B4 after passing through an oxidant chamber disposed on the cathode side of each of the cells D. Furthermore, cooling water flows in through a cooling water inlet B5, and is discharged through a cooling water outlet B5 after passing through a humidifying chamber F (disposed on the rear side of the plate B). In this arrangement, fuel gas is humidified by cooling water in the humidifying chamber F, and the polymer electrolyte membrane placed in the center of each cell D is humidified by the resulting humidified fuel gas. FIG. 9 shows a schematic diagram showing flows of fuel gas, of oxidant gas, and of cooling water.
In the case of the above-described polymer electrolyte fuel cell, the flow of fuel gas moving inside the humidifying chamber F is a co-flow with respect to the flow of cooling water moving inside the humidifying chamber F, and the flow of fuel gas moving inside the fuel chamber is a counter flow with respect to the flow of cooling water moving inside the fuel chamber, where the term co-flow signifies a flow in the same direction, and the term counter flow signifies a flow in the opposite direction (the same definitions apply hereinafter), provided that a direction of a flow is not limited to a vertical direction but may include a somewhat oblique direction and a horizontal direction, as well as a direction along a bent or otherwise irregular line, in consideration of the fact that passages have various configurations.
As described above, in the case of a polymer electrolyte fuel cell, electrochemical reaction accompanied by exothermic reaction takes place, and therefore, the temperature of that portion of each plate which faces one of the cells D becomes higher than that of the exterior periphery of the cell D. In the event that fuel gas is humidified by so arranging that the flow of fuel gas is a co-flow with respect to the flow of cooling water as mentioned above, then in the humidifying chamber, the temperature of cooling water at the outlet becomes higher than that at the inlet, and therefore it is possible to obtain saturated humidified fuel gas which has a high temperature (equivalent to the temperature of that portion of the cells D which has the highest temperature).
However, as can be seen from FIGS. 10(a) and (b), the temperature of that portion of the humidifying chamber F which is in the neighborhood of the humidified fuel gas outlet is 2 to 3xc2x0 C. lower than that of humidified fuel gas, and therefore, the water content in the humidified fuel gas is condensed. In the event that condensed water is generated, then fuel gas is hindered from flowing, resulting in the fuel cell performance being degraded. Furthermore, if it is so arranged that the flow of fuel gas moving inside the fuel chamber is a counter flow with respect to the flow of cooling water moving inside the fuel chamber, then the temperature at the outlet of the fuel chamber becomes lower than that at the inlet thereof. In the event that the temperature at the outlet of the fuel chamber lowers, then the water content in fuel gas becomes prone to be condensed, owing also to the fact that fuel gas is consumed at the outlet of the fuel chamber, thereby causing the fuel gas velocity to increase. The resulting condensed water hinders fuel gas from flowing, thereby causing the fuel cell performance to be degraded. Moreover, water is generated owing to reaction on the cathode side. In addition to humidification water, the resulting generated water constitutes still another factor for water condensation. This phenomenon can be prevented by reducing the utilization ratio of fuel or of oxidant, thereby increasing the fuel gas velocity at the fuel chamber outlet, but this practice is undesirable in terms of the fuel cell efficiency.
It is an object of the present invention, which was made for the purpose. of solving the problem of water being condensed in prior art polymer electrolyte fuel cells, is to provide a polymer electrolyte fuel cell wherein the directions of flows of fuel gas, of oxidant gas, and of cooling water are suitably combined, thereby enabling water condensation to be prevented.
By way of a means for achieving the above-mentioned object, the polymer electrolyte fuel cell of the present invention is so arranged that
a polymer electrolyte membrane having an anode on one side and a cathode on the other side constitutes a cell;
a fuel chamber with fuel gas flowing inside is provided on the anode side of the above-mentioned cell;
an oxidant chamber with oxidant gas flowing inside is provided on the cathode side of the above-mentioned cell;
the above-mentioned cell, the above-mentioned fuel chamber, and the above-mentioned oxidant chamber constitute a component cell;
a plurality of such component cells are laminated together to constitute a cell unit;
a plurality of such cell units are provided;
a humidifying chamber with cooling water flowing inside is provided between two adjacent cell units, thereby humidifying either fuel gas or oxidant gas, or both fuel gas and oxidant gas; and
the flow of fuel gas moving inside the above-mentioned fuel chamber, as well as the flow of oxidant gas moving inside the above-mentioned oxidant chamber, is a co-flow with respect to the flow of cooling water moving inside the above-mentioned humidifying chamber.
Furthermore, the above-mentioned polymer electrolyte fuel cell is so arranged that
the flow of fuel gas moving inside the above-mentioned humidifying chamber is a counter flow with respect to the flow of cooling water moving inside the above-mentioned humidifying chamber; and
the flow of fuel gas moving inside the above-mentioned fuel chamber is a co-flow with respect to the flow of cooling water moving inside the above-mentioned fuel chamber.
Moreover, in the above-mentioned polymer electrolyte fuel cell, fuel gas and oxidant gas are replaced with each other, thereby causing oxidant gas to be humidified in the humidifying chamber.
If it is so arranged that the flow of fuel gas moving inside the fuel chamber, as well as the flow of the oxidant gas moving inside the oxidant chamber, is a co-flow with respect to the flow of cooling water moving inside the humidifying chamber, then the resulting cooling water is used to cool the heat generated in the cells, and therefore, the temperature of cooling water at the outlet becomes higher than that at the inlet.
The temperature of the fuel gas or of the oxidant gas at the outlet of the fuel chamber or of the oxidant chamber, respectively, becomes higher than the temperature of the fuel gas or of the oxidant gas at the inlet of the fuel chamber or of the oxidant chamber, respectively, since the flow of fuel gas moving inside the fuel chamber, as well as the flow of the oxidant gas moving inside the oxidant chamber, is a co-flow with respect to the flow of cooling water moving inside the humidifying chamber. For this reason, fuel gas or oxidant gas is consumed at the outlet of the fuel chamber or of the oxidant chamber, respectively, and therefore, water condensation which would be caused by reduced flow velocity can be prevented.
In the event that a polymer electrolyte fuel cell is so arranged that the flow of fuel gas moving inside the humidifying chamber is a counter flow with respect to the flow of cooling water moving inside the humidifying chamber, and the flow of fuel gas moving inside the fuel chamber is a co-flow with respect to the flow of cooling water moving inside the fuel chamber; then the resulting cooling water is used to cool the heat generated in the cells, and therefore, the temperature of cooling water supplied is bound to be lower (by 5 to 20xc2x0 C.) than that of the cells. Since the flow of fuel gas moving inside the humidifying chamber is a counter flow with respect to the flow of cooling water moving inside the humidifying chamber, saturated humidified fuel gas can be obtained from the humidifying chamber such that the temperature of the above-mentioned fuel gas is lower than the temperatures of the cells and than the temperature of a portion in the neighborhood of the humidified fuel gas outlet. For this reason, humidified fuel gas can be supplied to the fuel chamber without causing any water content in the humidified fuel gas to be condensed.
Furthermore, since the flow of fuel gas moving inside the fuel chamber is a co-flow with respect to the flow of cooling water moving inside the fuel chamber is a co-flow with respect to the flow of cooling water moving inside the fuel chamber, the temperature of the fuel gas at the outlet of the fuel chamber becomes higher than the temperature of the fuel gas at the inlet of the fuel chamber. For this reason, fuel gas is consumed at the outlet of the fuel chamber, and therefore water condensation which would be caused by reduced flow velocity can be prevented.
In this connection, if it is so arranged that the flow of oxidant gas moving inside the oxidant chamber is a co-flow with respect to the flow of cooling water moving inside the oxidant chamber, then the temperature at the outlet of the fuel chamber becomes higher, and therefore, it is possible to increase the fuel utilization ratio while preventing water from being condensed at the outlet of the fuel chamber.
In the case of the polymer electrolyte fuel cell according to the present invention, the same results as above can be obtained in the event that the flow of fuel gas and the flow of oxidant gas are replaced with each other, thereby humidifying oxidant gas.